Young proteins experience more variable selection pressures than old proteins
Anchal Vishnoi1, Sergey Kryazhimskiy1, Georgii A. Bazykin2, Sridhar Hannenhalli3,4 and Joshua B. Plotkin1,4
-Author Affiliations
1 Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
2 Institute for Information Transmission Problems of the Russian Academy of Sciences, Moscow 127994, Russia;
3 Department of Genetics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
Abstract
It is well known that young proteins tend to experience weaker purifying selection and evolve more quickly than old proteins. Here, we show that, in addition, young proteins tend to experience more variable selection pressures over time than old proteins. We demonstrate this pattern in three independent taxonomic groups: yeast, Drosophila, and mammals. The increased variability of selection pressures on young proteins is highly significant even after controlling for the fact that young proteins are typically shorter and experience weaker purifying selection than old proteins. The majority of our results are consistent with the hypothesis that the function of a young gene tends to change over time more readily than that of an old gene. At the same time, our results may be caused in part by young genes that serve constant functions over time, but nevertheless appear to evolve under changing selection pressures due to depletion of adaptive mutations. In either case, our results imply that the evolution of a protein-coding sequence is partly determined by its age and origin, and not only by the phenotypic properties of the encoded protein. We discuss, via specific examples, the consequences of these findings for understanding of the sources of evolutionary novelty.
Footnotes
↵4 Corresponding authors.
E-mail jplotkin@sas.upenn.edu.
E-mail sridharh@pcbi.upenn.edu.
[Supplemental material is available online at http://www.genome.org.]
Article published online before print. Article and publication date are at http://www.genome.org/cgi/doi/10.1101/gr.109595.110.
Received April 23, 2010.
Accepted September 1, 2010.
Copyright © 2010 by Cold Spring Harbor Laboratory Press
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